Throughout the first truly global war, we can see from the present the large technological advancement and impact that the war had brought, as well as the effects of each. Each weapon created was to realistically make the war shorter, but sadly, prolonged the war and resulted in high casualty rates. Some of the most influential weapons would be listed below.
Machine guns: While the Machine gun had been around for a long time (Since the Mexican-American War & American Civil War, in which the Maxim machine-gun was used, these weapons was able to evolve for the better (and much more later on in history), making it more lethal, lighter, be able to hold more rounds, faster cooling system and firing rate, and much more other improvements. the machine guns (MG) was used widely on both sides, and were used as defensive weapons, being able to mow down charges by the opposing side through "no-mans land".
Tanks: Tanks were created by the British, and later copied by Germany and the USA. They had their first frightening appearance during the Battle of Somme, which was described as heavy sheet metal that rolled across the fields and deflected rounds. However, the first few prototypes that were created were flimsy, non-practical, and "easily destroyable". By the time the USA joined in 1917, many sides had been extensively using tanks, which led to the US developing their own variant, one that had a turrent, based on a tank known as the "Renault FT". These tanks were produced in massive numbers, and had a great impact on the resource-drained Central Powers.
Gas: Gas such as mustard gas (which are already banned today through the Geneva Convention) was also used extensively throughout the war. They were generally used without warning, and would lead to symptoms such as gagging, watery eyes, burning sensation, and even death, blindness, and others. Usually birds were used on both sides to detect the usage of gas, and soldiers had seconds to put on their gas masks.
Airplanes: Warplanes had a lesser impact on the war, but they still had their debut with glory. Biplanes and triplanes were extensively used by both sides, and could be seen doing reconnaissance, dropping bombs on enemy locations, and even have dogfights.
Submarines: While these also have been around since the Revolutionary War (the "Turtle"), subs were greatly expanded upon, especially by Germany and Austrio-Hungary. They were used extensively in the Mediterranean and the Atlantic Ocean to sink battleships, battlecruisers, and especially transport ships that brought vital resources and even troops to the western front.
While there were much more "new" technologies, these were some of the weapons that had the greatest impacts, and also were the ones that (except for gas) greatly expanded on during the latter years.
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